1. Field of the Invention
The present invention relates to an envelope warpage correcting device that is applicable to a printer printing an image on an envelope or a sheet such as plain paper, heavy paper, thin paper or mat paper, and is capable of correcting warpage (bending) occurring at a side of a rear end portion of each envelope when envelopes are stacked on a sheet feed table in a state of setting the rear end portion opposite to a flap portion formed in a front end portion of each envelope to a leading portion of envelope in a sheet feed direction.
2. Description of the Related Art
Generally, as a printer (image forming apparatus) for household use or business use that prints (forms) an image on an envelope or a sheet such as plain paper, heavy paper, thin paper or mat paper, an ink-jet printer, a stencil printer, a laser beam printer, a thermal transfer printer and the like have been frequently used.
In this type of printer, there is an envelope feeding apparatus that prevents a hard corner portion of envelope from damaging a master on a plate cylinder mounted in the stencil printer (e.g., Patent document 1: Japanese Published Unexamined Patent Application No. 2001-162917).
In the envelope feeding apparatus disclosed in Patent document 1, envelopes stacked on an envelope placement table are fed to a carrier line one-by-one. A pressing mechanism mounted in the carrier line flattens each of hard corner portions of envelope fed from the envelope placement table. Thereby, the envelope feeding apparatus prevents each hard corner portion of envelope from damaging a master on a plate cylinder at a time of feeding the envelope to the plate cylinder.
As shown in FIG. 1, an envelope S applied to the envelope feeding apparatus disclosed in Patent document 1 is formed into a pocket-like shape by overlapping a top sheet and a back sheet thereof. The envelope S has flap portions Sb extending from both side of the top sheet. The flap portions Sb are used to seal the envelope S after a card, a letter or the like is enclosed in the envelope S. When the flap portions Sb are folded toward a side of the back sheet to seal the envelope S, each of the flap portions Sb overlaps with the top sheet and the back sheet. This thickens the four corner portions Sa of the envelope S. Theses corner portions Sa are pressed by the pressing mechanism, which prevents them from damaging the master on the plate cylinder. However, the envelope feeding apparatus does not have any preparation for warpage occurring in the envelope.
As shown in FIGS. 2A and 2B, a rectangular envelope F in which a letter or the like is enclosed is formed into a pocket-like shape by overlapping a top sheet Fa and a back sheet Fb of the envelope F. The envelope F has a flap portion Fd which extends from the top sheet Fa at a side of a front end portion Fc, and a tab for sticking Ff which extends from the top sheet Fa at a side of a rear end portion Fe and is folded and stuck to a side of the back sheet Fb. This thickens the side of the rear end portion Fe of the envelope F because the side of the rear end portion Fe has the total of thicknesses of three sheets although the flap portion Fd has the thickness of one sheet.
Therefore, as shown in FIGS. 3A and 3B, when rectangular envelopes F are stacked on a sheet feed table K in a state where a top sheet Fa of each envelope F faces up, the thickness of envelopes F at a rear end portion side is remarkably larger than the thickness of envelops F at a front end portion side as the number of envelopes F stacked on the sheet feed table K increases. Due to this, warpage (bending-upward) in an upper direction occurs at a side of a rear end portion Fe of each envelope F.
A degree of warpage occurring at a side of a rear end portion Fe of an envelope F depends on an attribution of the envelope F. An attribution of envelope F is defined by the following parameter: a length of envelope F in a longitudinal direction, a width of envelope F perpendicular to the longitudinal direction, a thickness of envelope F, a material or the like.
In a case where a printer prints (forms) an image on an envelop F, envelopes F are generally stacked on a sheet feed table K in a state where a top sheet Fa of each envelope F faces up, in order to print a name and an address on the top sheet Fa of each envelope F. At this time, since rigidity at a rear end portion Fe is higher than rigidity at a flap portion Fd formed at a side of a front end portion Fc of each envelope F, the rear end portion Fe is set to a leading portion of the envelope F in a sheet feeding direction, and the flap portion Fd faces a direction opposite to the sheet feeding direction while not being folded.
In a state where a rear end portion Fe of each of envelopes F stacked on a sheet feed table K is set to a leading portion of the envelope F, the envelopes F are fed to a carrier line one-by-one and then carried toward an ink-jet head mounted in an ink-jet printer (not shown). If warpage (bending-upward) in an upper direction occurs at a side of a rear end portion Fe of each envelope F, there is a possibility that the rear end portion Fe collides against the ink-jet head to damage the ink-jet head because a space between the carrier line and the ink-jet head is narrow.
In order to solve the above-described technical problem, if an envelope F composed of double sheets (a top sheet Fa and a back sheet Fb) is subjected to correction processing to correct the warpage, the top sheet Fa and the back sheet Fb at the side of the rear end portion Fe of the envelope F are subjected to correction processing in an integrated manner for the initial period of time. However, when the top sheet Fa and the back sheet Fb at the side of the front end portion Fc of the envelope F are subjected to correction processing, highly-load is applied to one surface side. This raises a problem that wrinkles occur on the top sheet Fa only at the side of the front sheet Fc. This occurrence of wrinkles on the top sheet Fa only at the side of the front sheet Fc is a unique problem for envelope. A general-use card does not have this problem.
It is noted that in a case where warpage (bending-downward) in a down direction occurs at a side of a rear end portion Fe of the envelope F, there is not any possibility that the rear end portion Fe damage the ink-jet head because the rear end portion Fe does not collide against the ink-jet head.